题目描述：()

Reverse a singly linked list.

解题思路:

链表真讨厌，总是出错。头插法。

1 /** 2  * Definition for singly-linked list. 3  * struct ListNode { 4  *     int val; 5  *     ListNode *next; 6  *     ListNode(int x) : val(x), next(NULL) {} 7  * }; 8  */ 9 class Solution {10 public:11     ListNode* reverseList(ListNode* head) {12         if (head == NULL ) return head;13         14         ListNode dummy(-1);15         dummy.next = head;16         17         ListNode *prev = dummy.next;18         ListNode *cur = prev->next;19         while (cur != NULL) {20             prev->next = cur->next;21             cur->next = dummy.next;22             dummy.next = cur;23             cur = prev->next;24         }25         26         return dummy.next;27     }28 };